The present invention relates to piezo-electric crystal resonators in the form of a tuning fork, their manufacture and the test of their properties.
Resonators of the tuning fork type are constituted by a piezo-electric crystal, nearly always of quartz, which carries excitation electrodes on two parallel tines formed in the crystal, one on each side of an axis of symmetry. Such a crystal in the form of a tuning fork is cut in a conventional manner substantially in its X-Y plane, the tines being perpendicular to the X axis and forming an angle (angle of cut) with the Y axis. The application of an electrical field parallel to the X axis enables the tuning fork to be set in oscillation by the symmetrical flexure of the tines in their plane and enables these oscillations to be maintained at the natural frequency of the tuning fork. The performance of these resonators is closely connected with the respective masses of the two tines and with the symmetry of their deformation. Hence, it is of interest to detect possible asymmetry.
In order to detect the asymmetry, the invention proposes to detect the oscillations which are transmitted within the body of the crystal, beyond the tines, when there is not equilibrium between the deformations of one tine and those of the other tine and to make this detection by also causing a piezo-electric effect to occur in this region.